The invention relates to a vacuum belt conveyor for transferring a web threading tail in a web manufacturing machine, the belt conveyor comprising                a frame construction and at least two pulleys or rolls therein,        an air permeable belt loop, which is arranged around the rolls,        first vacuum means for providing a vacuum effect for the part of the belt loop that transports the web threading tail, and        second vacuum means for providing a vacuum effect in connection with the first roll of the said rolls.        
WO publication No. 03018909 discloses a vacuum belt conveyor according to the preamble, which is characterized by a vacuum effect in connection with the first roll. Thus the vacuum can be used to detach the web threading tail from a dryer surface, for example, without separate air blows or doctors. In the proposed tail threading device the vacuum is generated for the first roll with a venturi, which has a ring nozzle. The ring nozzle is located outside the vacuum belt conveyor, at the end of its pipe bracket. From the pipe bracket the vacuum is distributed by means of a bent pipe to a vacuum chamber arranged inside the frame construction and further to the first roll.
Locating the venturi at the end of the pipe bracket complicates the construction of the vacuum belt conveyor, which increases the purchase costs of the apparatus. In addition, the operating efficiency of the venturi is poor. The situation is further impaired by the distance of the venturi from the roll. In practice, a significant part of the vacuum discharges in the constructions, which further impairs the total operating efficiency of the venturi and increases the operating costs of the vacuum belt conveyor. Vacuum adjustment is also difficult and a great amount of compressed air is required for achieving a sufficient vacuum.